2D surface confined nanoporous molecular networks at the liquid-solid interface: a scanning tunneling microscopy study

Shengbin LeiLaboratory of Photochemistry and Spectroscopy and INPAC

KULeuven

Content

Introduction

Two strategies toward formation of flexible porous networks

Concentration controlGuest induced transformation

Conclusion

2D organic nanoporous networks

Ordered structures with cavities formed by organic molecules on top of a solid substrate.

Interactions involved

Hydrogen bonding

Metal-organic coordination

a 0.02mg/g

Van der Waals forces

2D analogues of Zeolite and Metal-organic frameworks

Application of the 2D nanoporous networks

Langmuir, Vol. 20, 2004, 9403.

Assembling of other organic molecules in a predefined mannerTemplate

Angew. Chem. Int. Ed. 2007, 46, 4089.

Molecular device

Challenges

Adjusting the pore sizeSize available: from < 1 nm to 5 nm

Adjust the pore size sequentially.Larger size possible?

Hosting molecular clusters

——beyond the state of art

nanovessels for chemical reactionLangmuir, Vol. 20, 2004, 9403.

Flexible porous network based on alkyl chain interdigitations

8.8 Å

Dehydrobenzo[12]annulene DerivativesDBA-OCn

Tahara K. et al. J. Am. Chem. Soc. 2006, 16613

Honeycomb structure

37

14.6

2.9

4.1

DBA-OC10

5.45.04.53.93.5Size of the poreCorner-to-Corner

6.35.95.55.04.6Repeating period (honeycomb)/nm

56 53 50 46 42 Percentage of pore /%

34.4 30.1 25.7 21.7 17.9 Area of unit cell /nm2

DBA-OC20DBA-OC18DBA-OC16DBA-OC14DBA-OC12

Parameters of the honeycomb structure formed by DBA-OCn

Advantage:

adjustable with high precision, ~ 2.5 Å

So in principle we can get nanopores with diameter ranging from 2.9 nm up to 5.4 nm using these DBAs as building blocks.

Effects of alkyl chain lengths (MS interaction)

OC10 OC12 OC14 OC16 OC18

In TCB, concentration 1 mg/ml

Two strategies

•Adjusting the concentration

•Guest induced transformation

Concentration dependent formation

The concentration of the solution determines the number of molecules on the surface.

Angew. Chem. Int. Ed. 2008, 47, 2964 –2968

10nm 10nm 10nm

0.20 mg/g 0.05 mg/g 0.01 mg/ga b c

high concentration low concentration

A series of STM images obtained with different concentration of DBA-OC16.

DBA-OC161.1×10-4 M 2.1×10-5 M 5.7×10-6 M

8% 80%

0.0000 0.0002 0.0004 0.0006 0.0008

0

20

40

60

80

100

θ /%

Concentration /M

OC12 OC14 OC16 OC18

0.00000 0.00001 0.00002 0.00003

102030405060708090

100110

θ /%

Concentration /M

OC18 OC16

ab

c

•General phenomena•In a certain concentration range the surface coverage of porous

structures show a linear dependence on concentration

A thermodynaomic model

solh µµ =soll µµ =

At equilibrium

and

[ ] [ ] KDBA

mDBA

hh ln1lnln +⎟⎟⎠

⎞⎜⎜⎝

⎛ −=⎟⎟

⎠

⎞⎜⎜⎝

⎛ θθ

6 8 10 12 142

4

6

8

10

12

14

ln{θ

h/[D

BA]}

ln{(1-θh)/[DBA]}

OC12

OC14

OC16

OC18

DBA-OC20

Nanopores with diameter ranging from 2.9 nm up to 7.5 nm could be formed.

The pore diameter could be tuned with precision of 0.25 nm.

DBA-OC30

5.0 × 10–6 mol/L 2.4 ×10-6 M

7.5 nm

Guest induced transformation

J. Am. Chem. Soc. 2008, in press.

Concentration of DBAs: 0.05 mg/mlWithout guest

Organic Porous Frameworks in 2D: tunable in size? Yes, but…

With guest

OC10 OC12 OC14 OC16 OC18 OC20

Tunable size of the cavities One to six nanographenes could be hosted.

Allows us to adjust the number of molecules, the geometry in the cluster.

DBA-OC16, different guest clusters, dimers to pentamers

Flexibility. The host matrix changes its structure in order to accommodate the adsorption of the guest clusters.

1 2 3 4 5 6 70

50

100

150

200

250

coun

t

number of molecules per cavity

OC18

OC20

Dynamics within the host-guest matrix

Dynamics of the guest inside the cavity

Migration of the guest between cavities

Dynamics of the host molecules

Rotation of the nanographene dimers inside the cavity of DBA-OC12

Note the length of the dimer is larger than the diameter of the cavity.3.8 nm vs 3.5 nm

Rotation of the clusters inside the cavity

These observations indicate the rotation angles are multiples of 60°.

The rotation of the guest cluster is a cooperative movement of the host-guest architecture.

Conclusion

2D nanoporous networks could be form with two different strategies: concentration control and guest induced transformation.

Tunable size and period, flexible

Beyond the art

Hosting molecular clusters, paved the way toward to use such nanoporous host matrices as nanoreactors

Acknowledgements

K.U.LeuvenProf. Steven De FeyterProf. Mark Van der AuweraerProf. Frans De Schryver

The Fund of Scientific Research – Flanders (FWO)

Institute for NanoscalePhysics and Chemistry (INPAC)

Financial support

Osaka Univ.Prof. Yoshito TobeDr. Kazukuni Tahara

Prof. Klaus MüllenDr. Xinliang Feng

Max Planck Institute for Polymer ResearchCollaborators Thank you for your attention !